7801

• UCREFRP Catalog Number: 7801
• Author: Valdez, R. A.
• Title: Synthesis of Winter Investigations of Endangered Fish in the Green River Below Flaming Gorge Dam.
• USFW Year: 1995.
• USFW - Doc Type: \
• Copyright Material: NO

during an early warming period, or a local rain spate--as in February of 1962. In postimpoundment
years, winter flows were higher and spikes representing early runoff or rainfall events were rarely
evident.
A monthly flow exceedance analysis (Bovee 1986) fora 12-year period before (1951-62) and
after (1977-8$) impoundment (Figure 4) shows that postimpoundment winter flows (December
through March) were higher than preimpoundment flows near Greendale. Average preimpoundment
winter flows exceeded 1,0(10 c£s (28 cros) twice, while flows in postimpoundmentyeacs exceeded 1,000
cfs in all years. Also, average monthly preimpoundment flows did not exceed 2,500 cfs (71 cros),
while postimpoundment flows exceeded that level in 33 to 58 percent of the years examined by
month.
Daily fluctuating releases are a significant attribute of Flaming Gorge Dam, determined largely
by power generation. To meet peaking power demand, dam releases are typically low at night and
high in morning and evening. These fluctuating releases are ameliorated with distance downstream
from the dam, and by the influence of major tributaries, such as the Yampa River.
Average and extreme hourly releases from Flaming Gorge Dam for January and February of
1987 and 1988 (Figure 5) illustrate a large daily variation in discharge. Flow was typically lowest
between midnight and 0600 hours, and highest between 0800 hours and 2000 hours. These extreme
daily operational data indicate that the Green River below Flaming Gorge Dam experienced a two
to five-fold change in daily flow during these two winters, with maximum change of 800 to 4,000 cfs.
Attenuating or dissipating downstream effects of these flow changes from Flaming Gorge Dam
were determined for four release scenarios, under ice-free conditions, using the Streamtlow thesis
And Regulation Reservoir (SSARR) model (U.S. Army Corps of Engineers 1972). 'This model was
used to determine changes in stage (water surface elevation) at three gaged locations downstream
from the dam; Mitten Park (108 km, 67 miles below), Jensen Bridge (174 km, 108 miles below), and
Ouray Bridge (260 km, 162 miles below) (Figure 6). The four scenarios were based on a release of
800 cfs (23 cros) followed by 4,200 cfs (119 cros), or maximum powerplant variation, for durations of
1, 2, 4, or 8 hours. These flows approximated minimum and maximum operational releases from
Flaming Gorge Dam in winter, 1986-87 and 1987-88, and provided conditions to illustrate maximum
changes in stage.
Maximum stage change occurred when flows of 800 cfs were followed by 4,200 cfs for a
duration of 8 hours. This resulted in a stage change of 58 cm at Mitten Park, 46 cm at Jensea, and
15 crn at Ouray. The 4hour scenario produced stage changes of 46, 37, and 12 cm, respectively.
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